1. Field of the Invention
The present invention relates to a method and apparatus for performing radio bearer mapping in a wireless communications system, and more particularly to a method and apparatus for ensuring that an user equipment of the wireless communications system uses a proper multiplexing mode, so as to enhance transmission efficiency.
2. Description of the Prior Art
The third generation (3G) mobile communications system has adopted a Wideband Code Division Multiple Access (WCDMA) wireless air interface access method for a cellular network. WCDMA can provide high frequency spectrum utilization, universal coverage, and high quality, high speed multimedia data transmission. The WCDMA method also meets all kinds of QoS requirements simultaneously, providing diverse flexible two-way transmission services and better communication quality to reduce transmission interruption rates.
For the universal mobile telecommunications system (UMTS), the 3G communications system comprises User Equipment (UE), the UMTS Terrestrial Radio Access Network (UTRAN), and the Core Network (CN). Communications protocols utilized include Access Stratum (AS) and Non-Access Stratum (NAS). AS comprises various sub-layers for different functions, including Radio Resource Control (RRC), Radio Link Control (RLC), Media Access Control (MAC), Packet Data Convergence Protocol (PDCP), and Broadcast/Multicast Control (BMC). The sub-layers mentioned, and their operating principles, are well known in the art, and detailed description thereof is omitted. RRC is a Layer 3 communications protocol, and is the core of the AS communications protocol. All radio resource information exchange, radio resource configuration control, QoS control, channel transmission format configuration control, packet segmentation/concatenation processing and control, and NAS protocol transmission processing is performed by the RRC layer.
The RRC layer is located in the Radio Network Controller (RNC) of the UTRAN and the UE, and is primarily used to manage and maintain packet switching and sequencing of a Uu Interface. The RRC layer performs radio resource control in the following manner. After the RRC of the UE obtains various measurement results from the MAC and the Physical Layer, the RRC generates a Measurement Report from the various measurement results. After processing by the RLC, the MAC, and the Physical Layer, the Measurement Report is sent to the RRC of a network, e.g. UTRAN. After a Radio Resource Assignment message sent from the RRC of the network is received, the RRC of the user equipment can perform lower layer control and setting based on a result of resolving the message, e.g. setting the operation mode, packet length, and encryption method of the RLC layer, setting the channel multiplexing mapping method and channel transmission format of the MAC, and setting the operating frequency, spreading code, transmission power, synchronization method, and measurement items of the Physical Layer.
Between the user equipment and the network, the RRC layer uses RRC Messages, also known as signaling, to exchange information. RRC Messages are formed from many Information Elements (IE) used for embedding necessary information for setting, changing, or releasing protocol entities of Layer 2 (RLC, MAC) and Layer 1 (Physical Layer), thereby establishing, reconfiguring, or releasing information exchange channels to perform data packet transportation. Through RRC Messages, the RRC layer can embed control signals needed by an upper layer in the RRC Message, which can be sent between the NAS of the user equipment and the CN through the radio interface to complete the required procedures.
From the standpoint of the RRC, all logical data communication exchange channels, be they for providing data transmission exchange to the user or for providing RRC layer control signal transmission exchange, are defined in the context of a Radio Bearer (RB). In the user end, the RB comprises one unidirectional or a pair of uplink/downlink (UL/DL) logic data transmission exchange channels. In the network, the RB comprises one unidirectional or a pair of uplink/downlink logic data transmission exchange channels.
In order to enhance transmission efficiency, the RRC layer of the UE can select appropriate multiplexing options according to the IE “RB mapping info” provided by the network, so as to determine statuses of UL/DL transport channels. When the UE operating in a CELL_DCH (Cell Dedicated Channel) state conforms to specified rules (e.g. when the UE receives the IE “RB mapping info”, when specified transport channels are added or deleted, when the UE performs a cell reselection or a state transition, or when the UE releases an RB), the UE shall set the multiplexing option of a frequency-division-duplex (FDD) RB according to a multiplexing option selection process 10 of the prior art shown in FIG. 1. The multiplexing option selection process 10 comprises the following steps, where DCH, HS-DSCH, E-DCH, and DSCH mean Dedicated Channel, High Speed Downlink Shared Channel, Enhanced Dedicated Transport Channel, and Downlink Shared Channel.                Step 100: Start.        Step 102: Determine whether the FDD RB has a multiplexing option with transport channel type “DCH+HS-DSCH” for the DL, and with transport channel type “E-DCH” for the UL. If true, go to Step 118; else, go to Step 104.        Step 104: Determine whether the FDD RB has a multiplexing option with transport channel type “DCH+HS-DSCH” for the DL, and with transport channel type “DCH” for the UL. If true, go to Step 118; else, go to Step 106.        Step 106: Determine whether the FDD RB has a multiplexing option with transport channel type “DCH+DSCH” for the DL. If true, go to Step 120; else, go to Step 108.        Step 108: Determine whether the FDD RB has a multiplexing option with transport channel type “HS-DSCH” for the DL, and with transport channel type “E-DCH” for the UL. If true, go to Step 118; else, go to Step 110.        Step 110: Determine whether the FDD RB has a multiplexing option with transport channel type “HS-DSCH” for the DL, and with transport channel type “DCH” for the UL. If true, go to Step 118; else, go to Step 112.        Step 112: Determine whether the FDD RB has a multiplexing option with transport channel type “DSCH” for the DL. If true, go to Step 120; else, go to Step 114.        Step 114: Determine whether the FDD RB has a multiplexing option with transport channel type “DSCH” for the DL, and with transport channel type “DCH” for the UL. If true, go to Step 118; else, go to Step 116.        Step 116: Determine whether the FDD RB has a multiplexing option with transport channel type “DCH” for the DL, and with transport channel type “E-DCH” for the UL. If true, go to Step 118; else, go to Step 122.        Step 118: Use the corresponding multiplexing option for RB mapping, and go to Step 122.        Step 120: Determine that the UE behavior is unspecified, and go to Step 122.        Step 122: Determine whether the FDD RB has a multiplexing option with transport channel type “DCH” for the DL, and with transport channel type “DCH” for the UL. If true, go to Step 124; else, go to Step 126.        Step 124: Use the multiplexing mode corresponding to the multiplexing option for RB mapping.        Step 126: Do not use the multiplexing mode corresponding to the multiplexing option for RB mapping.        Step 128: End.        
Therefore, the multiplexing option selection process 10 must undergo Step 122, whether the FDD RB conforms to one of the multiplexing options mentioned in Steps 102 to 116 or not. That is, the UE must determine if the FDD RB has a multiplexing option with transport channel type “DCH” for the DL and UL. Meanwhile, when the FDD RB has the multiplexing option with transport channel type “DCH” for the DL and UL, the UE uses the multiplexing mode corresponding to the multiplexing option for RB mapping; when the FDD RB does not have the multiplexing option with transport channel type “DCH” for the DL and UL, the UE does not use the multiplexing mode corresponding to the multiplexing option for RB mapping. In other words, the UE must check the conditions of Step 122 to select the multiplexing mode. In such a situation, the UE can only use the low data rate transport channel corresponding to Step 122 for RB mapping even if there are other multiplexing options with higher data rate transport channels available. Therefore, the steps before Step 122 become redundant and invalid, and the UE cannot reach a proper transmission rate.
In short, since the multiplexing option selection process 10 must undergo Step 122, the UE cannot use multiplexing modes corresponding to Steps Step 102 to 116 when the FDD RB has a multiplexing option with transport channel type “DCH” for the DL and UL, leading to low transmission efficiency.